(1) Field of the Invention
The present invention relates to a semiconductor device, and more particularly, to a semiconductor device in which the withstandability against destruction by an electrostatic voltage applied to an external terminal is improved.
(2) Description of the Prior Art
A conventional TTL type integrated circuit device comprises an input protection circuit for each inner TTL type logic circuit. Each input protection circuit comprises a Schottky barrier type clamp diode connected between an external input terminal and a power terminal, e.g., ground. The clamp diode turns on when a negative voltage is applied to the external input terminal due to, for example, noise, and protects the inner TTL type logic circuit.
When an excessive positive voltage is applied to the external input terminal due to, for example, electrostatic voltage, the Schottky barrier type clamp diode enters a breakdown state, to protect the internal circuits by preventing the application of a high voltage thereto.
However, in the above-mentioned conventional semiconductor device, if a relatively high positive voltage is applied to the external input terminal, the Schottky barrier type clamp diode is sometimes permanently destroyed, and is short-circuited due to an excessive current flowing therethrough.